Sparking plug electrode



Patented Aug. 3, 1943 UNITED STATES PATENT OFFICE SPARKING PLUGELECTRODE pany of Delaware No Drawing. Application May 27, 1942, SerialNo. 444,745. In Great Britain January 31, 1941 2 Claims.

This invention relates to sparking plugs for internal combustionengines. In internal combustion engines of high efficiency, such asthose used in aeroplanes, the sparking plugs often have electrodes ofprecious metal. As a rule, alloys of platinum, such as those withiridium, rhodium and the like, are used and are made from metals havingthe purity generally available commercially at the present time.

It has been found that sparking plugs made from such alloys are liableto fail in service under severe operating conditions, so that their lifeis not as long as it might be. The primary object of this invention" isto overcome this drawback.

It is an object of this invention to provide an improved sparking plugelectrode having a longer life than those now used commercially.

It is a further object of this invention to provide an improvedplatinum-rhodium sparking plug electrode.

of such an element or elements in the metal or alloy does not exceedabout 0.01%, and preferably it is less than about 0.005%.

I have found that in order that the electrodes shall give the bestservice, in particular prolonged life, under severe working conditions,it is of the utmost importance that the alloys from which the electrodesare made should be as nearly as possible free from impurities whichwould produce embrittlement, either alone or with any other element orelements contained in the alloy or taken up by it in service. issurprising because the total amount of impurities present in preciousmetals used for this purpose at present is so small that it would not beexpected that they would have any effect at all upon electrodes madefrom the precious metals. I have found, however, that the elementsplatinum, rhodium, iridium and osmium in the forms in which they arenormally available commercially contain enough impurities to shorten thelife of an electrode made from them; An alloy which is often used isthat consisting of about 90% platinum and about 10% rhodium, and it hasnow been found that commercial rhodium introduces tellurium and bismuthinto the alloy in harmful amounts.

This

In my invention I make the electrodes from one of the metals platinum,rhodium, iridium and osmium, or an alloy of one or more of these,containing so little of any element or elements which, even in a smallquantity, would produce trode made from 10% rhodium and 90% platinum.These tellurium and bismuth contents are normally introduced into thealloys as impurities of the rhodium. I have found that increased lifemay be obtained by employing platinum free from tellurium and bismuthtogether with rhodium containing 0.005% bismuth (as determined byspectrographic analysis) and 0.024% tellurium (as determinedmicrochemically). Then in the alloy containing 90% platinum and 10%rhodium the tellurium and bismuth contents are 0.0024% and 0.0005%respectively, making about 0.003% in all. Naturally the purer the alloy,the longer the life that the electrode is likely to have. Other elementsbesides tellurium and bismuth which may produce embrittlement and whichmay constitute impurities in the precious metals commercially availableare the other elements of the sulphur group (sulphur and selenium), theother elements of the phosphorus group (phosphorus, arsenic andantimony), lead, tin and silicon. Of course, in the example given abovecare is taken. that these other embrittlement producing elements areeithercompletely absent or present at the most in amounts that cannot bedetermined by ordinary chemical analysis, I

- In producing electrodes according tothe inpurities may be used. Forinstance, rhodium may beconverted into a solution of rhodium chloride,precipitated from this as rhodium potassium nitrite and convertedinto'rhodium potassium chloride, being recovered from a solution of thissalt by reduction with formic acid. Platinum may be purified moresimply, for example by dissolving the metal in aqua regia andprecipitating it as ammonium chloroplatinate.

The electrodes may be made from alloys containing other metals inaddition to those mentioned. In particular the alloys may containpalladium, ruthenium, gold and silver, but these metals can be andnormally are obtained commercially in a sufiiciently pure state not toneed re-refining, Moreover the alloys may contain base metals of highmelting point, e. g. tungsten, molybdenum, copper and nickel, but in anycase one or more precious metals predominate, that is to say, thepredominating part of the alloy consists of precious metals although nosingle precious metal may amount to as much as 50% of the alloy.

I claim:

1. As an article of manufacture, a sparking plug electrode made fromamember selected from the group consisting of the metals platinum,rhodium, iridium and osmium and alloys predominantly containing at leastone of said metals, the predominant metal of said electrode beingre-refined, and the said metalor alloy being so devoid of elements fromthe group consisting of sulphur, selenium, tellurium, phosphorus,arsenic, antimony, bismuth, lead, tin, and silicon that the presencethereof cannot be determined with certainty by chemical analysis andthat the total amount of elements from said group is less than 0.01%,said electrode being characterized by improved service life compared toa similar electrode containing elements of said group in excess of about0.01%.

2. As an article of manufacture, a sparking ,plug electrode made from amember selected from the group consisting of the metals platinum,rhodium, iridium and osmium and alloys predominantly containing at leastone of said metals, the predominant metal of said electrode beingre-refined, and the said metal or alloy be-

